Study on the dynamical spin-crossover phenomenon coupled with spinm and charge, and its multifunctionalities

在本项目中，我们合成了二硫代xalato桥接的铁混合价配合物（n- c_nh_ <2n+1>）_4N[Fe^<II>Fe^<III>(dto)_3] (n=3-6, dto=C_2O_2S_2)，并研究了自旋熵驱动的电荷转移相变，其中电子在Fe^<II>和Fe^<III>位点之间的阿伏伽德罗常数转移，以及（n- c_3h_7）_4N[Fe^<II>Fe^<III>(dto)_3]在6.5 K下的铁磁转变。当n=3和n= 4时发生电荷转移相变，而当n=5和n= 6时在300 K和4 K之间不发生电荷转移相变。在[Fe^<II>Fe^<III>(dto)_3]_∞的二维蜂窝网络结构中，电荷转移相变和铁磁相变显著依赖于六角形环的大小。阳离子尺寸的增大使蜂窝环膨胀，使Fe^<II> (S=2)和Fe^<III> (S=1/2)的高温相稳定。相反，蜂窝环的收缩稳定了Fe^<II> (S=0)和Fe^<III> (S=5/2)的低温相，这得到了外部压力对电荷转移相变的支持。为了用光照射控制四桥铁混价体系的磁性和电子态，我们合成了一种光敏有机-无机杂化体系（SP）[Fe^<II>Fe^<III>(dto)_3] (SP=spiropyran)，并研究了光诱导对磁性的影响。紫外照射使螺吡喃在（SP）[Fe^<II>Fe^<III>(dto)_3]中由封闭结构变为开放结构。螺吡喃的光致变色诱导了[Fe^<II>Fe^<III>(dto)_3]_∞二维蜂窝网络结构的电荷转移相变，并改变了铁磁转变温度。

In this project, we have synthesized dithiooxalato-bridged iron mixed-valence complexes, (n-C_nH_<2n+1>)_4N[Fe^<II>Fe^<III>(dto)_3] (n=3-6, dto=C_2O_2S_2) and investigated a spin-entropy driven charge transfer phase transition around 120 K, where the electrons of Avogadro's constant transfer cooperatively between the Fe^<II> and Fe^<III> sites, and a ferromagnetic transition at 6.5 K for (n-C_3H_7)_4N[Fe^<II>Fe^<III>(dto)_3]. The charge transfer phase transition takes place for n=3 and 4, while it does not take place between 300 K and 4 K for n=5 and 6. The charge transfer phase transition and the ferromagnetic transition remarkably depend on the hexagonal ring size in the two-dimensional honeycomb network structure of [Fe^<II>Fe^<III>(dto)_3]_∞. The increase of cation size expands the honeycomb ring, which stabilizes the higher temperature phase with Fe^<II> (S=2) and Fe^<III> (S=1/2). Contrary, the contraction of the honeycomb ring stabilizes the lower temperature phase with Fe^<II> (S=0) and Fe^<III> (S=5/2), which was supported by the external pressure effect on the charge transfer phase transition.In order to control the magnetic properties and the electronic state in the dto-bridged iron mixed-valence system by means of photo-irradiation, we have synthesized a photo-sensitive organic-inorganic hybrid system, (SP)[Fe^<II>Fe^<III>(dto)_3] (SP=spiropyran), and investigated the photo-induced effect on the magnetic properties. The UV irradiation changes the structure of spiropyran from the closed form to the open one in (SP)[Fe^<II>Fe^<III>(dto)_3]. The photochromism in spiropyran induces the charge transfer phase transition in the two-dimensional honeycomb network structure of [Fe^<II>Fe^<III>(dto)_3]_∞, and changes the ferromagnetic transition temperature.